1. Field of the Invention
The present invention is related generally to a method and apparatus for reinforcing roofs in subterranean excavations such as mines, subway tunnels, and the like, and more particularly, is directed towards a combination drill bit and roof bolt utilized in a bore hold formation and roof reinforcement technique.
2. Description of the Prior Art
There are many different apparatus and techniques utilized for strengthening roofs in subterranean structures such as coal mines, subway tunnels, or the like. The techniques in general use require a drill or bore hole to be formed in the roof structure as a separate and distinct step from installing the strengthening member.
In one such technique, the bore hole is adpated to house mechanical expansion gripping members to permit a bolt to be tightened down against a face of the rock structure to therefore reinforce same.
Another widely used technique involves the insertion of a rod or bolt within the drill hole and the subsequent placement of an adhesive or grouting material thereabout while the bolt is tensioned. The inner or embedded end of the rod or bolt is securely anchored at the end of the hole. Typically, this is done with an expansion shell anchor or by cementing in the embedded end prior to tensioning. The outer end of the rod or bolt may be provided with threads, a nut, and a face-plate washer. The nut is tightened-down to pull up the plate against the front face of the structure in order to tension the rod. The tensioning is applied prior to and maintained during the hardening of the adhesive.
As noted above, in either of the well-known techniques, as exemplified for example in U.S. Pat. Nos. 3,877,235 and 3,695,045, a bore hole must be drilled to accommodate the roof bolt. The actual drilling of the hole and subsequent insertion of the bolt, tensioning, and application of grouting is, of course, automated to every extent possible in order to expedite each installation cycle and thereby save valuable time.
However, it may be appreciated that at least two different types of tools must be utilized during each such installation cycle; namely, a high-speed drill for forming the bore hole, and a bolter for insertion and tensioning of the roof bolt. This handling of many tools necessarily takes time.
Another handling factor to consider is the frequency with which the drill bits utilized to form the bore holes must be changed. Due to the highly abrasive nature of the rock structures, and the ease with which the sharpened blades wear down, they must frequently be replaced, which requires yet another handling step that interrupts the cycle. Also, deleterious effects may result from using a dull drill bit which, perhaps due to economics or inadvertence, has not been replaced.